Stanley #20 compass plane locking screw thread?

[sploo]

I've picked up an old Stanley #20 compass plane (showing the 1893 patent),
but it's missing the small screw that can be used to lock the curve
adjustment (i.e. stop the large wheel rotating).

I happened to see a Record version at a show and the screw appeared to be
a #10-24 (#10 UNC, 24 tpi); but the Stanley has a finer thread.

I've subsequently tried a #10-32 (#10 UNF, 32 tpi) but that wouldn't go in
either.

Neither M4 or M5 fit (not that it was likely to be a metric thread
anyway). I'm assuming it's not going to be Whitworth (BSW) as it's a US
made tool (I think).

With a Vernier, I make the tapped hole approx 4.5mm in diameter. Could
anyone throw out any other suggestions as to what the thread might be?

 

[AndyT]

I've been and measured the screw on my Stanley 20 which is probably newer than yours but is also quite old. I make it 3/16" diameter but 28 tpi. That combination doesn't appear on my ordinary comparison chart of thread sizes, so I reckon it's one of those lovely obsolete standards which only surfaces on old Stanley kit.
If you just want to use the plane, you could drill out to 5mm and tap M6. If you want an original screw to fit, you might need to do some hunting. Do you have a metalworking lathe?

 

[sploo]

That sounds plausible. A bit of searching tells me there is a UNS (Special) standard; which contains #10-28 (.19 inch, 28tpi). That would be very close.

Sadly no metalworking lathe.

 

[rxh]

Did you manage to find a suitable screw? If not I may be able to make one for you.

 

[sploo]

Did you manage to find a suitable screw? If not I may be able to make one for you.

Thanks. AndyT kindly not only made me one, but sent it for free!

I got the required length wrong, but I should be able to get it working. Andy was spot on with the thread.

There's surely a market in making of some of these weird old screws Stanley used. I know I'd be more than happy to pay a few quid for them, so it's really a case of how economical it would be for a DIYer with a lathe to make batches for sale.

Note to self: I'd love a metalworking lathe :wink: